Hybrid circuit interrupter

ABSTRACT

A hybrid circuit interrupter is provided, having a set of contacts in a vacuum environment and another set of contacts in an insulating fluid, such as oil, or gas or the like, environment connected in series and disposed in one compact enclosure. During closing the contacts in the insulating liquid or gas are closed after the contacts in the vacuum have closed. During an opening operation the contacts in the vacuum chamber separate first and then the contacts in the chamber containing the insulating fluid or gas separate. Thus, the circuit is completed in the insulating liquid or gas environment and the circuit is opened in the vacuum environment. With the hybrid circuit interrupter fully opened two serially related gaps are provided in the circuit interrupter. One of the contacts in the chamber containing the insulating fluid or gas is rigidly mechanically connected to one of the contacts in the vacuum chamber. A single operating stroke opens or closes the hybrid circuit interrupter. The contacts used in the vacuum chamber can be constructed from material having low chopping characteristics so that high voltages are not induced in the electrical circuit during interruption. The contacts used in the chamber containing the insulating fluid, such as oil or gas, can be constructed from material having good non-welding characteristics so as not to weld upon interrupter closing and to be easily opened without the use of complicated and expensive weld breaking mechanisms.

United States Patent [191 Harrold [111 3,814,882 June4, 1974 1. HYBRIDCIRCUIT INTERRUPTER Ronald T. Harrold, Murrysville, Pa.

[73] Assignee: Westinghouse Electric Corporation,

1 Pittsburgh, Pa.

[22] Filed: July 25, 1973 [21] Appl. No.: 382,421

[75] inventor:

52 us. c1... 200/1 44 B, zoo/14s B, zoo/150 E Primary Examiner-Robert S.Macon Attorney, Agent, or Firm-H. G. Massung [57] ABSTRACT A hybridcircuit interrupter is provided, having a set of contacts in a vacuumenvironment and another set of contacts in an insulating fluid, such asoil, or gas or the like, environment connected in series and disposed inone compact enclosure. During closing the contacts in the insulatingliquid or gas are closed after the contacts in the vacuum have closed.During an opening operation the contacts in the vacuum chamber separatefirst and then the contacts in the chamber containing the insulatingfluid or gas separate. Thus, the circuit is completed in the insulatingliquid or gas environment and the circuit is opened in the vacuumenvironment. With the hybrid circuit interrupter fully opened twoserially related gaps are provided in the circuit interrupter. One ofthe contacts in the chamber containing the insulating fluid or gas isrigidly mechanically connected to one of the contacts in the vacuumchamber. A single operating stroke opens or closes the hybrid circuitinterrupter. The contacts used in the vacuum chamber can be constructedfrom material having low chopping characteristics so that high voltagesare not induced in the electrical circuit during interruption. Thecontacts used in the chamber containing the insulating fluid, such asoil or gas, can be constructed from material having good non-weldingcharacteristics so as not to weld upon interrupter closing and to beeasily opened without the use of complicated and expensive weld breakingmechanisms.

11 Claims, 4 Drawing Figures l HYBRID CIRCUIT INTERRUPTER BACKGROUND OFTHE INVENTION fluid, such as oil or SR; (sulfur hexafluoride), and thecircuit is opened in a vacuum chamber. The circuit interrupter disclosedutilizes the principle of closing on contacts .in an environment wherethe contacts do not weld on closing and opening in a vacuum environmenton contacts having good chopping characteristics so as to minimizecurrent chopping upon opening.

Contact welding on closing and current chopping on opening are twoproblems associated with vacuum interrupters. Contact welding causesrapid contact erosion and necessitates an expensive release mechanism toinsure that the contactswill open when required. While current choppinginduces undesirable high volt ages in the circuit being interrupted.Other types of interrupters such as oil and SP or the like do notexperience contact welding on closing but generally experience rapidcontact erosion on opening. Conversely, vacuum switches experiencelittle contact erosion on opening due to their excellent arcextinguishing properties.

A typical prior art type vacuumcircuit interrupter generally comprisesan evacuated insulation envelope. The contacts are movable between aclosed position in which the contacts are engaged and an open positionwhere the contacts are separated and an arcing gap is establishedtherebetween. An arc is initiated between the contact surfaces when thecontacts move into or out of engagement of the circuit in which theinterrupter is energized. As the contacts are brought together the arcsthat are formed melt some of the metallic contact material. After thecontacts are brought together under high pressure, engagement welds maybe formed between the contact surfaces due to the melted contactmaterial formed during arcing. Current surges also occur in the firstfew milliseconds of contact closing and these can alsocause contactwelding. The magnitude of the force required to break the welds so thatthe contacts can be opened depends upon many factors including the arcvoltage, the current, the contact area,

and the contact material. These welds are objectionable since theyinterfere with easy movement of the separable contacts and may result infailure of the vacuum interrupter to open.

Another difiiculty that is encountered with some prior art contacts invacuum interupters is that the materials used have an excessive tendencyto chop under low current conditions. This sharp chop in current caninduce extremely high. voltages across inductive de vices connected inthe circuit being interrupted and such over voltages can lead todestruction of the circuit components. For an effective circuitinterrupter there should not be an excessive current chop on the circuitopening'One of the best materials for opening is copper, but this weldseasily on contact closing. it is felt that the present invention hassignificant advantages over prior art circuit interruptcrs in that thecircuit is closed on a material and in 'an environment, such as oil orSF that assures there will be no contact welding and the circuit isopened on a material such as copper in a vacuum environment to assurerapid interruption without current chopping.

- SUMMARY OF THE INVENTION This invention discloses a hybrid circuitinterrupter construction which effectively closes in an environmentwhich will provide good non-welding characteris tics and opens in anenvironment such as a vacuum on a material such as copper, which doesnot cause excessive current chopping and which has good interruptingcharacteristics. Essentially the contacts of a vacuum interrupter areconnected in series and controlled in sequence with another set ofcontacts disposed in an insulating fluid such as oil, SP or the like.The vacuum contacts close first without current flowing thus there canbe no welding of the vacuum chamber contacts and then the contacts inthe insulating liquid fluid or gas close to complete the circuit withoutcontact welding. On opening, the vacuum contacts open first to interruptthe current without current chopping and little contact erosion, andthen the contacts in the insulating liquid fluid or gas part withouthaving to interrupt current and therefore experience no contact erosion.In this way, the vacuum contacts can neverweld and hardly erode and thecontacts in the other insulating media would experience little contacterosion.

In one embodiment of the invention both sets of contacts are disposed ina single insulation enclosure. This improves operation of the vacuuminterupter and the insulating fluid interrupter. One operator stroke,without other'mechanical linkage can open and close both sets ofcontacts. Closing in oil, SP or the like and opening in a vacuum can beaccomplished by using two circuit breakers. However, this would beuneconomical, involve longer opening and closing times, and presentsynchronization problems. In the disclosed invention a first chamberhaving a vacuum and a second chamber containing an insulating fluid,such as oil, SP or the like are formed within an insulating housing. Thehousing can be of a generally tubular construction with a vacuum chamberformed at one end of the housing and the oil or SF chamber formed at theother end of the housing. Both ends of the housing are closed bymetallic end caps. The vacuum chamber is separated from the chambercontaining the insulating medium by a metallic separator. A fixedcontact is supported by a conducting rod which is attached to one end ofthe insulating housing. A first movable contact is attached to a movableoperating rod which extends through the other end of the insulatinghousing. Disposed between the fixed contact and the first movablecontact is a centrally disposed contact assembly comprising a secondmovable contact disposed in the vacuum chamber, a third movable contactdisposed in the chamber containing the insulating fluid and a movableconducting rod connecting the second and third movable contacts. Thesecond and third movable contacts and the movable conducting rod arerigidly connected so as to form the centrally disposed contactsassembly. 1

As the circuit interrupter is closed the first movable contact movesinto engagement with the second movable contact and moves the centrallydisposed contact assembly so that the third movable contact engages thefixed contact and completes an electrical path through the circuitinterrupter. On interrupter opening the first movable contact initiallyseparates from the second movable contact and then the third movablecontact separates from the fixed contact so that gaps are formed betweenthe first movable contact and the second movable contact and between thethird movable contact and the fixed contact. Thus when the circuitinterrupter is in the open position two serially related gaps are formedin the circuit interrupter.

The circuit interrupter disclosed in the instant application has severaladvantages over some prior art interrupters, such as having no weldingof the vacuum contacts and thus requiring no special operating mechanismto break contact welds. There is very little erosion of the contacts andby proper selection of contact material used in thevacuum chamber,current chopping on opening can be held to a minimum. The chambercontaining an insulating fluid such as oil or a gas such as SP can beconstructed to be easily opened so that these contacts can be inspectedand maintained. A high voltage rating is possible since two completeserially related breaks are present when the interrupter is in theopened position. Only one operator is required to open both sets ofcontacts and full contact pressure is maintained on both sets ofcontacts when in the closed position. In one compact design, the contactopening advantages of vacuum interrupters are combined with the contactclosing advantages of other types of circuit breakers.

It is an object of this invention to provide a circuit interrupter whichcompletes an electric circuit through a set of contacts disposed in aninsulating fluid or gas and opens the electric circuit through a set ofcontacts disposed in a vacuum.

It is an object of this invention to provide a circuit interrupterhaving two serially related sets of contacts disposed in a singlecompact housing; one set of contacts being disposed in a vacuumenvironment and the other set of contacts being disposed in aninsulating fluid or gas environment.

It is another object of this invention to provide a circuit interrupterhaving two sets of contacts in series which can be opened or closed by asingle operator stroke, and which maintains full contact pressure onboth sets of contacts.

BRIEF DESCRlPTlON OF THE DRAWINGS Further advantages of the presentinvention will be readily apparent upon reading the followingdescription taken in conjunction with the drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingsand more particularly to FIG. 1, there is shown a circuit interrupter 10embodying the teachings of the present invention. The circuitinterrupter 10 comprises an insulating envelope 12 formed of glass or asuitable ceramic material and, a

pair of metallic end caps 14 and 16. A central metallic partition 15divides the insulating envelope 12 into two chambers, 11 and 13, andrenders the top portion of insulating envelope 12 between end cap 16 andpartition 15 vacuum tight. The top portion of insulating envelope 12 isthus fomied into a vacuum chamber 13. The vacuum chamber 13 under normaloperating conditions is lower than 10 so that the mean free path ofelectrons will be longer than the potential breakdown distance withinthe vacuum chamber 13.

Disposed within the vacuum chamber 13 are a first movable contact 20 anda second movable contact 22. As shown in FIG. 1, when these contacts 20and 22 are separated there is an arcing gap 24 formed therebetween. Thetop movable contact 20 is movable into and out of engagement withcontact 22. Contact 20 is attached to a conducting operating rod 28. Theconducting operating rod 28 is suitably mounted for movement along thelongitudinal axis of the insulating envelope 12. The movable operatingrod 28 projects through an opening 30 in end cap 16 and is connected tosuitable operating means (not shown) which moves contact 20 generallyalong the longitudinal axis of insulating envelope 12.

As shown in FIG. 1, a flexible metallic bellows 32 is secured in sealingrelationship at its respective opposite ends to movable operating rod 28and to the opening 30 in end cap 16. The flexible metal bellows 32provides a seal about the rod 28 to allow for movement of the rod 28without impairing the vacuum inside vacuum chamber 13.

Movable contact 22 is secured to connecting rod 50, which is formed froma material having good electrical conduction properties, by suitablemeans such as welding or brazing. Conductive connecting rod 50 issuitably mounted for movement along the longitudinal axis of the tubularinsulating envelope 12. The movable connecting rod 50 projects throughan opening 31 in partition member 15 and extends into chamber 11 at thebottom side of insulating envelope 12. Partition member 15 separatesvacuum chamber 13 from a second chamber 11, formed at the bottom ofinsulating envelope 12 and containing an insulating fluid such as oil orgas such as SF Disposed within chamber 11 are a third movable contact 52and a stationary contact 54.

As shown in FIG; 1, a second flexible metallic bellows 62 is secured insealing relationship at its respective opposite ends to conductingmovable connecting rod 50 and opening 31 in the partition member 15. Theflexible metal bellows 62 provides a seal about the rod 50 to allow formovement of the rod 50 along the longitudinal axis of insulatingenvelope [2 without impairing the vacuum inside vacuum chamber 13.Movable contact 52' is rigidly secured to the end of connecting rod 50,which projects into chamber 11, by suitable means such as welding orbrazing. The stationary contact 54 is secured to a conducting supportrod 56 by suitable means such as welding or brazing. The support rod 56passes through and is secured to end cap 16 by suitable means, such aswelding or brazing.

Coupled to the free end of the operating rod 28, suitable actuatingmeans (not shown) is provided for driving the movable contact 20 intoengagement with movable contact 22 which in turn moves connecting rod 50and attached contact 52 into engagement with stationary contacts 54 soas to close the circuit interrupter l0.

While in the closed position a'continuous current path is providedthrough the circuit interrupter 10. The continuous current path extendsthrough conducting rod 56, stationary contact 54, contact 52, connectingrod 50, contact 22, contact 20 and conducting operating rod 28. Theactuating-means is also capable of returning the movable contact 20 toits open position so as to open the interrupter 10. With the circuitinterrupter in the fully opened position as shown in FIG. 1 a gap 64exists between contacts 52 and 54 and another gap 24 exists betweencontacts 20 and 22. Thus in the fully opened position, two seriallyrelated gaps, 24 and 64, exist in the interrupter giving a high voltagewithstand level. i

Due to the short distances to be moved and the high dielectric strengthof vacuum, circuit interrupter 10 can be opened very rapidly, whencompared with an oil or gas type circuit breaker. When during currentinterruption circuit interrupter 10 opens, contacts and 22 disposedwithin the vacuum chamber l3-separate at the beginning of circuitinterruption and a metallic arc initiates between the separated contacts20 and 22. The

are formed across gap 24 serves as a vehicle for current conductionuntil the arc is extinguished. In an alternating current circuit the arcis usually extinguished near the first current zero of the alternatingcurrent wave. The are that is established across the arcing gap 24between the contacts 20 and 22 when they are opened, vaporizes and meltssome of the contact material. The vapors are dispersed from the arcinggap 24 towards the inside ofthe insulating envelope 12 which forms aportion of vacuum chamber 13. The internal surfaces of the insulatingenvelope 12'within-vacuum chamber 13 are protected from the condensationof the arc generated metallic vapor and particles thereon by means of atubular metallic shield 36. The tubular metallic shield 36 is supportedon the insulating envelope l2 and preferably electricallyisolatedfromboth end cap 16 and partition member 15. This shield acts tointer-.

cept and condense arcgenerated metallic vapor and particles before theycan reach the internal surfaces of the vacuum chamber 13. A cupshapedshield 42 is attached to the movable operating rod 28 and partiallysurrounds flexible metal bellows 32 to prevent the bellow 32 from beingbombarded by are generated metallic vapors and particles. At the otherend of the vacuum chamber another cup shaped shield 44 is attached tothe conducting movable connecting rod and surrounds a portion offlexible metal bellows 62 to prevent bellows 62 frombeing bombarded byare generated metallic vapors or particles.

' As shown in FIG. 2,'when the circuit interrupter 10 is in the fullyclosed position, contact 20 is in engagement with contact 22 and contact52 is in engagement with contact 54. During initial closing of circuitinterrupter 10 as shown in FIG. 3, contact 20 initially engages contact22 and as operating rod 20 continues to move to the left the centrallydisposed contact assembly 51 comprising contacts 22, and 52, andconnecting rod 50 are moved to the left until contact 52 engagesstationary contact 54 and a continuous current path is establishedthrough interrupter 10. As can be seen in FIG. 3, contacts 20 and22during initial closing are in engagement while a gap 64 still existsbetweenc'ontacts 52 and 54. Due to thepresence of gap 64 there can be nocurrent flowing through the interrupter 10 when contacts 20 and 22engage during initial closing of interrupter 10. Thus, since contacts 20and 22, which are disposed in the vacuum chamber 13, close under nocurrent conditions there can be no welding of contacts 20 and 22 duringinterrupter 10 closing. Since thkre is no welding of the contacts 20 and22 disposed in the vacuum chamber 13 during circuit interrupter l0closing, special weld break mechanisms are not required to open theinterrupterlO and separate contacts 20.and 22.

Final closing of the circuit through interrupter 10 is thus accomplishedas the centrally disposed contact assemblies 51 is moved to the left,and contacts 52 and 54 which are disposed in chamber lll engage. Chamber11 is filled with an insulating fluid, such as oil, SR, or the like, andcontacts closing in these environments do not weld. Thus, theinterrupter 110 can be closed as shown in FIG. 2 without the danger ofeither contacts 20 and 22 or contacts 52 and 54 being welded together.Thus, the interrupter 10 can be opened and closed with a simplifiedoperating mechanism, not requiring expensive weld breaking apparatus. Itshould be noted that since contact sets 20-22 and 52-54 when inengagement areserially related the full contact pressure applied by theoperating mechanism is provided between each pair of contacts 2022 and52-54. Only one operation is necessary to close both set of contacts andno synchronization problems are present. Also, all contacts can beclosed without theme of complicated interlinking mechanisms as would berequired if a separate vacuum interrupter and oil interrupter wereconnected serially.

The pressure internal of chamber 11 acts on the bellows 62 and thecentrally disposed contact assembly 51 to urge the centrally disposedcontact assembly 51 to the open position when the operating mechanismmoves contact 20 to the open position.

During an opening operation contact 20 initially separates from contact22 as shown in FIG. 4. Due to the high dielectric strength of the vacuumin chamber 13 and a quick recovery time the current through interrupter10 is normally interrupted at the first current zero, after contacts 20and 22 separate. Thus the circuit is interrupted in a vacuum environmentwhich has excellent arcextinguishing properties. Thus, there is verylittle arcing during circuit opening in chamber 11, which would causerapid deterioration of contacts 52 and 54. After the operating mechanismmoves contact 20 to the open position as shown in H0. 4, the internalpressure of chamber ll upon the centrally disposed contact assembly 51urges the contact assembly 51 to the open position. As shown in FIG. 4,a dashpot and stop arrangement can be added to limit the speed andtravel of contact assembly 51. A disc can be attached to connecting rod50 and fit inside a tubular member 72 so as to act as a dashpot andlimit the opening speed of contacts 52 and 54. Orifices 74 may beprovided in disc 70 to determine the speed at which contact 52 will moveto the open position. Stop 76 may also be provided to limit the travelof contact assembly 51. The stop 76 will limit the travel of contactassembly 51 so that two gaps 24 and 64 will be maintained internal ofinterrupter 10. By varying the opening speed of the oil or gas disposedcontacts 52 and 54 the interruption can be shared by vacuum contacts 20and 22 and the oil or gas contact 52 and 54. This can aid in controllingcurrent chopping.

The end cap 14 is attached to the insulating envelope 12 by suitablemeans such as bolts 80 which provide for easy removal of end cap 14.Allowing end cap 14 to be easily removed permits ready access to chamber11 and allows for maintenance and inspection of contacts 52 and 54. Thusmaintenance of the non-vacuum part of interrupter is facilitated. it canbe seen that an interrupter is provided having a construction in whichthe opening advantages of vacuum interrupters are combined with theclosing advantage of other type circuit interrupters. Since there is noproblem with contact welding a simplified operating mechanism issufficient without the necessity of complicated and expensive releaseand weld breaking mechanisms. Contacts and 22 can be formed of amaterialhaving good current chopping characteristics such as copper toassure that upon contact interruption there will be minimal currentchop. High voltage ratings are possible with the structure taught inthis invention since two interrupting gaps are placed in series ininterrupter 10. The simplified operating mechanism can open and closeboth pairs of contacts 20, 22 and 52, 54 without additional leverage ormechanical linkage. With theconstruction taught in this invention thereis no synchronization problem with the sequence of opening and closingof the interrupter l0.

What is claimed is:

1. A circuit interrupter comprising:

a vacuum chamber being vacuum tight and having a high vacuum' formedtherein;

a first set of contacts disposed within said vacuum chamber and beingmovable between an open position and a closed position;

an insulating fluid chamber containing an insulating fluid having a highdielelctric strength;

a second set of contacts disposed in said insulating fluid chamber andbeing movable between an open position and a closed position;

said first set of contacts being connected in series with said secondset of contacts so that said first set of contacts and said second setof contacts both must be closed to close said circuit interrupter; and;

operating means for closing and opening said circuit interrupter wherebyduring a closing operation of said circuit interrupter said first set ofcontacts close and then after a time delay said second set of contactsclose and during an opening operation of said circuit interrupter saidfirst set of contacts opens and then after a time delay said second setof contacts opens.

2. A circuit interrupter comprising:

a vacuum chamber;

a first movable contact disposed within said vacuum chamber;

a second movable contact disposed within said vacuum chamber;

said first movable contact and said second movable contact beingrelatively movable between a closed position in which said first movablecontact and said second movable contact are in engagement and an openposition in which said first movable contact is separated from saidsecond movable contact to establish a gap therebetween;

an insulating fluid chamber containing an insulating fluid having a highdielectric strength;

a stationary contact disposed within said insulating fluid chamber;

a third movable contact disposed within said insulating fluid chamberand being movable between a closed position in engagement with saidstationary contacts and an open position spaced from said stationarycontacts to establish a gap therebetween;

electrical conductor means connecting said second movable contact tosaid third movable contact;

said first movable contact, said second movable contacts, said thirdmovable contact, and said stationary contact being connected in series;

operating means for moving the contacts of said circuit interrupterbetween an open position, in which said first movable contact is spacedfrom said second movable contact and said third movable contact isspaced from stationary contact. and a closed position, in which saidfirst movable contact engages said second movable contact and said thirdmovable contact engages said stationary contact, providing a continuouscurrent path through said circuit interrupter; and wherein,

said operating means during a closing operation of said circuitinterrupter initially causes said first movable contact to engage saidsecond movable contact and later causes said third movable contact toengage said stationary contact, and during an opening operation of saidcircuit interrupter initially causes said first movable contact toseparate from said second movable contact and later causes said thirdmovable contact to separate from said stationary contact to provide twoserially related gaps in said circuit interrupter.

3. A circuit interrupter as claimed in claim 2 comprising;

an insulating housing;

said insulating housing forming a portion of said vacuum chamber and aportion of said insulating fluid chamber.

4. A circuit interrupter as claimed in claim 2 wherein:

said insulating housing comprises a generally tubular shaped portionformed from an insulating material; and

partition means disposed in said insulating tubular portion of saidinsulating housing perpendicular to the longitudinal axis of saidinsulating housing to divide said housing into a first portion whichforms part of said vacuum chamber and a second portion which forms partof said insulating fluid chamber.

5. A circuit interrupter as claimed in claim 2, wherein said electricalconductor means comprises a rigid electrical conductor.

6. A circuit interrupter as claimed in claim 5, wherein said rigidelectrical conductor is formed as a generally rod-shaped member havingsaid second movable contact attached rigidly to one end and said thirdmovable contact attached rigidly to said respective opposite ends so asto rigidly position said second movable contact with respect to saidthird movable contact.

7. A circuit interrupter as claimed in claim 6, wherein said secondmovable contacts and said third movable contacts and said rigidelectrical conducting means are formed as an integral part.

8. A circuit interrupter as claimed in claim 2, wherein said firstmovable contact and said movable contact are 10 movable contact areformed from copper.

11. A- circuit interrupter as claimed in claim 2, wherein saidinsulating fluid chamber comprises an access cover and removablefastening means to hold said access cover in position so that accesscover can be easily removed to provide access to sadi stationary contactand said third contact.

1. A circuit interrupter comprising: a vacuum chamber being vacuum tightand having a high vacuum formed therein; a First set of contactsdisposed within said vacuum chamber and being movable between an openposition and a closed position; an insulating fluid chamber containingan insulating fluid having a high dielelctric strength; a second set ofcontacts disposed in said insulating fluid chamber and being movablebetween an open position and a closed position; said first set ofcontacts being connected in series with said second set of contacts sothat said first set of contacts and said second set of contacts bothmust be closed to close said circuit interrupter; and, operating meansfor closing and opening said circuit interrupter whereby during aclosing operation of said circuit interrupter said first set of contactsclose and then after a time delay said second set of contacts close andduring an opening operation of said circuit interrupter said first setof contacts opens and then after a time delay said second set ofcontacts opens.
 2. A circuit interrupter comprising: a vacuum chamber; afirst movable contact disposed within said vacuum chamber; a secondmovable contact disposed within said vacuum chamber; said first movablecontact and said second movable contact being relatively movable betweena closed position in which said first movable contact and said secondmovable contact are in engagement and an open position in which saidfirst movable contact is separated from said second movable contact toestablish a gap therebetween; an insulating fluid chamber containing aninsulating fluid having a high dielectric strength; a stationary contactdisposed within said insulating fluid chamber; a third movable contactdisposed within said insulating fluid chamber and being movable betweena closed position in engagement with said stationary contacts and anopen position spaced from said stationary contacts to establish a gaptherebetween; electrical conductor means connecting said second movablecontact to said third movable contact; said first movable contact, saidsecond movable contacts, said third movable contact, and said stationarycontact being connected in series; operating means for moving thecontacts of said circuit interrupter between an open position, in whichsaid first movable contact is spaced from said second movable contactand said third movable contact is spaced from stationary contact, and aclosed position, in which said first movable contact engages said secondmovable contact and said third movable contact engages said stationarycontact, providing a continuous current path through said circuitinterrupter; and wherein, said operating means during a closingoperation of said circuit interrupter initially causes said firstmovable contact to engage said second movable contact and later causessaid third movable contact to engage said stationary contact, and duringan opening operation of said circuit interrupter initially causes saidfirst movable contact to separate from said second movable contact andlater causes said third movable contact to separate from said stationarycontact to provide two serially related gaps in said circuitinterrupter.
 3. A circuit interrupter as claimed in claim 2 comprising;an insulating housing; said insulating housing forming a portion of saidvacuum chamber and a portion of said insulating fluid chamber.
 4. Acircuit interrupter as claimed in claim 2 wherein: said insulatinghousing comprises a generally tubular shaped portion formed from aninsulating material; and partition means disposed in said insulatingtubular portion of said insulating housing perpendicular to thelongitudinal axis of said insulating housing to divide said housing intoa first portion which forms part of said vacuum chamber and a secondportion which forms part of said insulating fluid chamber.
 5. A circuitinterrupter as claimed in claim 2, wherein said electrical conductormeans comprises a rigid electrical conductor.
 6. A circuit interrupTeras claimed in claim 5, wherein said rigid electrical conductor is formedas a generally rod-shaped member having said second movable contactattached rigidly to one end and said third movable contact attachedrigidly to said respective opposite ends so as to rigidly position saidsecond movable contact with respect to said third movable contact.
 7. Acircuit interrupter as claimed in claim 6, wherein said second movablecontacts and said third movable contacts and said rigid electricalconducting means are formed as an integral part.
 8. A circuitinterrupter as claimed in claim 2, wherein said first movable contactand said movable contact are formed from a material having goodnon-chopping characteristics and said third movable contact and saidstationary contacts are formed from a material having good non-weldingcharacteristics.
 9. A circuit interrupter as claimed in claim 2, whereinsaid insulating fluid chamber contains an insulating fluid comprising agas.
 10. A circuit interrupter as claimed in claim 2, wherein said firstmovable contact and said second movable contact are formed from copper.11. A circuit interrupter as claimed in claim 2, wherein said insulatingfluid chamber comprises an access cover and removable fastening means tohold said access cover in position so that access cover can be easilyremoved to provide access to sadi stationary contact and said thirdcontact.